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Research Papers

Review and Analysis of Cross Flow Heat Exchanger Transient Modeling for Flow Rate and Temperature Variations

[+] Author and Article Information
Tianyi Gao

Department of Mechanical Engineering,
SUNY-Binghamton University,
Suite 1211,
Center of Excellence Building,
85 Murray Hill Road,
Binghamton, NY 13902
e-mail: Tgao1@binghamton.edu

James Geer, Bahgat Sammakia

Department of Mechanical Engineering,
SUNY-Binghamton University,
Center of Excellence Building,
85 Murray Hill Road,
Binghamton, NY 13902

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received February 27, 2015; final manuscript received July 9, 2015; published online September 10, 2015. Assoc. Editor: Pedro Mago.

J. Thermal Sci. Eng. Appl 7(4), 041017 (Sep 10, 2015) (10 pages) Paper No: TSEA-15-1057; doi: 10.1115/1.4031222 History: Received February 27, 2015; Revised July 09, 2015

Heat exchangers are important facilities that are widely used in heating, ventilating, and air conditioning (HVAC) systems. For example, heat exchangers are the primary units used in the design of the heat transfer loops of cooling systems for data centers. The performance of a heat exchanger strongly influences the thermal performance of the entire cooling system. The prediction of transient phenomenon of heat exchangers is of increasing interest in many application areas. In this work, a dynamic thermal model for a cross flow heat exchanger is solved numerically in order to predict the transient response under step changes in the fluid mass flow rate and the fluid inlet temperature. Transient responses of both the primary and secondary fluid outlet temperatures are characterized under different scenarios, including fluid mass flow rate change and a combination of changes in the fluid inlet temperature and the mass flow rate. In the ε-NTU (number of transfer units) method, the minimum capacity, denoted by Cmin, is the smaller of Ch and Cc. Due to a mass flow rate change, Cmin may vary from one fluid to another fluid. The numerical procedure and transient response regarding the case of varying Cmin are investigated in detail in this study. A review and comparison of several journal articles related to the similar topic are performed. Several sets of data available in the literatures which are in error are studied and analyzed in detail.

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References

Figures

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Fig. 1

Data center thermal management. Several viable options for liquid cooling and hybrid cooling design using cross flow heat exchangers: (a) rear-mounted heat exchanger, (b) top-mounted heat exchanger, (c) bottom-mounted heat exchanger, and (d) side-mounted heat exchanger (top view) [1].

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Fig. 2

Effectiveness curves of the dry cooler, simulation results and experimental data, with the Cmin variation effect included [18] (8 GPM = 0.000504 m3/s)

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Fig. 3

(a) A schematic representation of cross flow heat exchanger and (b) symmetric 2D model geometry

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Fig. 6

Experimental validation [16]

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Fig. 4

Model validation with the analytical solution in Ref. [6] for step input inlet temperature with E = R = 1 and V = 0 and fluid mass flow rate: rc = rh = 1 [9]

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Fig. 5

Model validation with the analog solution in Ref. [15] for both NTU 1–1.5 and NTU 1.5–1 cases [19]

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Fig. 7

Numerical solution verification with two published numerical studies. Two single mass flow rate variation cases (with E = R = V = NTU = 1): case 1: rh = 0.8 and rc = 1 and case 2: rh = 0.5 and rc = 1 [14].

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Fig. 8

Outlet temperature transient response under different hot fluid mass flow rate step changes using the present procedure: (a) cold fluid and (b) hot fluid (NTU = 1, E = 1, R = 1, and V = 1)

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Fig. 9

Repetition of the results in Ref. [14] for rh = 3, rh = 2, rh = 0.8, and rh = 0.5 cases

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Fig. 10

Outlet temperature transient response under different hot fluid mass flow rate step changes using the numerical procedure presented in Ref. [14]: (a) cold fluid and (b) hot fluid

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Fig. 11

Steady-state temperature results comparison for different hot fluid mass flow rate variations

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Fig. 12

Outlet temperature transient response under combination of hot fluid inlet temperature step change and different hot fluid mass flow rate step changes: (a) hot fluid and (b) cold fluid (NTU = 1, E = 1, R = 1, and V = 1)

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Fig. 13

Outlet temperature transient response under combination of hot fluid inlet temperature step change and hot fluid mass flow rate step change (rh = 2), effect of NTU

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Fig. 14

Outlet temperature transient response under combination of hot fluid inlet temperature step change and different cold fluid mass flow rate step changes: (a) hot fluid and (b) cold fluid (NTU = 1, E = 1, R = 1, and V = 1)

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Fig. 15

Outlet temperature transient response under combination of hot fluid inlet temperature step change and hot fluid mass flow rate step change (rh = 2), effect of E

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